Polymer compositions having high thermal conductivity and dielectric strength and molded packaging assemblies produced therefrom

ABSTRACT

A polymer composition having high thermal conductivity and dielectric strength is provided. The polymer composition comprises a base polymer matrix and a thermally-conductive, electrically-insulating material. A reinforcing material such as glass can be added to the composition. The polymer composition can be molded into packaging assemblies for electronic devices such as capacitors, transistors, and resistors.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication 60/338,127 having a filing date of Nov. 13, 2001.

BACKGROUND OF THE INVENTION

[0002] The present invention generally relates to polymer compositionshaving high thermal conductivity and dielectric strength. Particularly,the polymer composition comprises a base polymer matrix and athermally-conductive, electrically-insulating material. The inventionalso encompasses molded packaging assemblies for electronic devices suchas capacitors, transistors, and resistors. The invention furtherincludes methods for making such packaging assemblies.

[0003] Electronic devices such as semiconductors, microprocessors,circuit boards, capacitors, transistors, and resistors can generate asubstantial amount of heat that must be removed in order for the deviceto function properly. For example, a 1000-Ohm resistor in a 120 Voltcircuit must dissipate 14 Watts of energy during operation. If theresistor is installed in a densely packaged circuit board, it is highlysusceptible to overheating that can destroy the resistor and othercomponents in the board. The industry has attempted to address thisproblem in a variety of ways.

[0004] For example, the electronic device may have a metallic outercover. The cover can be made from aluminum or copper and installed ontothe device. Although a metallic cover can dissipate a substantial amountof heat, it is electrically-conductive. Thus, an electrically-insulatinglayer must be placed between the device and cover. Although theelectrically-insulating layer provides good electrical isolation, it isgenerally a poor thermal conductor. Thus, the electrically-insulatinglayer can prevent effective heat conduction between the device anddevice cover.

[0005] It is also common to employ heat pipes having a metal casing tohelp remove heat from a heat-generating object. In addition, metal heatspreaders in a laptop computer may be employed for transferring anddissipating heat. While these metal components can effectively dissipateheat and have good mechanical strength, they are typicallyelectrically-conductive. Therefore, these components must beelectrically insulated from the heat-generating components so as not tointerfere with their electrical operation.

[0006] The industry uses thermally-conductive polymeric compositions inan attempt to overcome some of the negative aspects found with metallicheat transfer components. These thermally-conductive polymericcompositions have some advantages over metallic components. For example,the polymeric compositions can be injection-molded into parts havingcomplex geometries such as interface pads which are placed between theheat-generating device and heat sink. The injection-molding process iseffective, because it can produce a “net-shape” part. The final shape ofthe part is determined by the shape of the mold cavity. No furthermachine tooling is required to produce the final shape of the part. Incontrast, such additional machine processing is often needed for shapingmetallic parts, and this processing can be costly and time-consuming. Inaddition, polymer materials are often lighter and less costly thanmetallic parts.

[0007] McCullough, U.S. Pat. No. 6,251,978 (the '978 Patent) discloses athermally and electrically-conductive, composite material that isnet-shape moldable. The '978 Patent discloses a composition containing:a) between 30 to 60% by volume of a polymer base matrix, b) between 25to 60% by volume of an electrically-conductive filler having arelatively high aspect ratio of at least 10:1, and c) between 10 to 25%by volume of an electrically-conductive filler having a relatively lowaspect ratio of 5:1 or less. The '978 Patent discloses that thematerials employed for the high aspect and low aspect ratio fillers maybe selected from the group consisting of aluminum, alumina, copper,magnesium, brass, and carbon.

[0008] As described in the '978 Patent, fillers used in conventionalpolymer compositions are typically thermally andelectrically-conductive. For example, when a polymer base matrix isloaded with carbon fibers and metallic flakes to enhance the thermalconductivity of the composition, the composition is also quiteelectrically-conductive. As a result, parts made fromthermally-conductive polymer compositions also generally require anadditional electrically-insulating layer when placed in contact withelectrically-conductive, heat-generating devices.

[0009] In view of the foregoing problems, it would be desirable to havea polymer composition with high thermal conductivity as well as highdielectric and mechanical strength. Such a composition should be capableof being molded into a packaging assembly for electronic devices. Thepresent invention provides such a polymer composition. The inventionalso encompasses molded packaging assemblies for electronic devices. Theinvention further includes methods for making such packaging assemblies.

SUMMARY OF THE INVENTION

[0010] This invention relates to relates to polymer compositions havinghigh thermal conductivity and dielectric strength. The polymercomposition comprises: a) 20% to 80% by weight of a polymer matrix, andb) 20% to 80% by weight of a thermally-conductive,electrically-insulating ceramic material. The polymer composition mayfurther comprise 3% to 50% by weight of a reinforcing material. Thepolymer matrix can be a thermoplastic or thermosetting polymer. Thethermally-conductive, electrically-insulating ceramic material can beselected from the group consisting of alumina, calcium oxide, titaniumoxide, silicon oxide, zinc oxide, silicon nitride, aluminum nitride,boron nitride, and mixtures thereof. The reinforcing material can beglass, inorganic minerals, or other suitable material.

[0011] The present invention also encompasses an electronic devicepackage assembly, comprising: i) an electronic device having a frontside, rear side, left side, right side, bottom side, and top side; ii) amolded cover disposed about said electronic device and in thermalcommunication with at least said front side, rear side, left side, rightside, and top side of said electronic device, and iii) at least two wireleads, said wire leads emanating from said electronic device andprotruding through said molded cover. The molded cover is made from thethermally-conductive, electrically-insulating polymer composition ofthis invention. The present invention further includes a method ofmanufacturing an electronic device package assembly. The method involvesthe steps of providing an electronic device and molding thethermally-conductive, electrically-insulating polymer composition ofthis invention over the device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The novel features that are characteristic of the presentinvention are set forth in the appended claims. However, the preferredembodiments of the invention, together with further objects andattendant advantages, are best understood by reference to the followingdetailed description taken in connection with the accompanying drawingsin which:

[0013]FIG. 1 is a perspective view of the device cover and electronicpackage assembly of the present invention;

[0014]FIG. 2 is a top view of the device cover and electronic package ofthe present invention of FIG. 1;

[0015]FIG. 3 is a cross-sectional view of the electronic device alongline 3-3 of FIG. 1; and

[0016]FIG. 4 is a perspective view of an alternative embodiment of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention relates to polymer compositions having highthermal conductivity and high dielectric and mechanical strength. Theinvention also encompasses molded packaging assemblies for electronicdevices. The invention further includes methods for making suchpackaging assemblies.

[0018] A thermoplastic polymer selected from the group consisting ofpolycarbonate, polyethylene, polypropylene, acrylics, vinyls,fluorocarbons, polyamides, polyesters, polyphenylene sulfide, and liquidcrystal polymers such as thermoplastic aromatic polyesters can be usedto form the matrix. Alternatively, thermosetting polymers such aselastomers, epoxies, polyimides, and acrylonitriles can be used.Suitable elastomers include, for example, styrene-butadiene copolymer,polychloroprene, nitrile rubber, butyl rubber, polysulfide rubber,ethylene-propylene terpolymers, polysiloxanes (silicones), andpolyurethanes.

[0019] The thermally-conductive, electrically-insulating ceramicmaterial imparts thermal conductivity to the non-conductive polymericmatrix. The thermally-conductive, electrically-insulating ceramicmaterial can be selected from the consisting of alumina, calcium oxide,titanium oxide, silicon oxide, zinc oxide, silicon nitride, aluminumnitride, boron nitride, and mixtures thereof. Mixtures of such materialsare also suitable. As discussed in more detail below, carbon materialssuch as carbon fibers and flakes are not used in the compositions of thepresent invention since such materials tend to detrimentally effect thecomposition's electrically-insulating properties.

[0020] The thermally-conductive, electrically-insulating material may bein any suitable form such as granular powder, particles, whiskers, andfibers. The particles can have a variety of structures. For example, thegrains can have flake, plate, rice, strand, hexagonal, or spherical-likeshapes.

[0021] The ceramic material may have a relatively high aspect (length tothickness) ratio of about 10:1 or greater. Alternatively, the ceramicmaterial may have a relatively low aspect ratio of about 5:1 or less.For example, boron nitride grains having an aspect ratio of about 4:1can be used. Both low aspect and high aspect ratio ceramic materials canbe added to the polymer matrix.

[0022] While not wishing to be bound any theory, it is believed that thepolymer compositions of this invention have good electrical insulationproperties due to their ability to prevent localized heat build-up anddegradation of the polymer. Particularly, the failure of plastics inmost electrical insulation or dielectric property tests can be describedas a result of the following phenomena:

[0023] 1) localized charge build-up,

[0024] 2) localized heating due the localized charge,

[0025] 3) degradation of the polymer due to excessive heat,

[0026] 4) eventual conversion of a portion of the polymer to carbon, and

[0027] 5) the carbon (electrically conductive) provides an electricalcurrent path and thus failure of the material as an electricalinsulator.

[0028] In contrast, the polymer compositions of this invention have goodthermal conductivity; thus, they prevent the localized build-up of heatand degradation of the polymer.

[0029] The optional reinforcing material can be glass, inorganicminerals, or other suitable material. Preferably, a reinforcing materialis used, because it strengthens the polymer matrix and enhances thedielectric properties of the composition. The reinforcing material ispreferably chopped glass.

[0030] The polymer matrix preferably constitutes about 20 to about 80%by weight, and the thermally-conductive, electrically-insulatingmaterial preferably constitutes about 20 to about 80% by weight of thecomposition. The reinforcing material, if added, constitutes about 3% toabout 50% by weight of the composition.

[0031] The thermally-conductive, electrically-insulating material andreinforcing material are intimately mixed with the non-conductivepolymer matrix to form the polymer composition. The loading of thethermally-conductive, electrically-insulating material imparts thermalconductivity and dielectric strength to the polymer composition. Theloading of the reinforcing material enhances the mechanical strength ofthe composition. If desired, the mixture may contain additives such as,for example, flame retardants, antioxidants, plasticizers, dispersingaids, and mold-releasing agents. The mixture can be prepared usingtechniques known in the art. Preferably, the ingredients are mixed underlow shear conditions in order to avoid damaging the structure of thethermally-conductive, electrically-insulating materials.

[0032] Preferably, the polymer compositions have a thermal conductivityof greater than 3 W/m° K and more preferably greater than 22 W/m° K.These heat conduction properties allow the finished article toeffectively dissipate heat from a heat-generating source. Thecomposition also has good electrical-insulation properties. For example,the polymer composition preferably has a volume resistivity of greaterthan 1.0×10¹⁶ ohms-cm and a surface resistivity of greater than 7.0×10¹⁴ohms; a dielectric strength (breakdown voltage) of at least 44,000 on aspecimen having a thickness of about 0.05 inches; a comparative trackingindex (Volts) of at least 500; an Arc Resistance of at least 300seconds; and a hot wire ignition of greater than 120 seconds asdescribed in further detail in the Examples below.

[0033] The polymer composition can be molded into any desired articleusing a melt-extrusion, injection-molding, casting, or other suitableprocess. An injection-molding process is particularly preferred. Ingeneral, this process involves loading pellets of the composition into ahopper. The hopper funnels the pellets into a heated extruder, whereinthe pellets are heated and a molten composition (liquid plastic) forms.The extruder feeds the molten composition into a chamber containing aninjection piston. The piston forces the molten composition into a mold.The mold may contain two molding sections that are aligned together insuch a way that a molding chamber or cavity is located between thesections. The material remains in the mold under high pressure until itcools. The shaped article is then removed from the mold. The shapedarticles of the present invention have several advantageous properties.Preferably, the article has a thermal conductivity of greater than 3W/m° K, and more preferably it is greater than 22 W/m° K. Further, thearticle preferably has the electrical insulation properties as describedabove for the polymer composition.

[0034] Further, the shaped articles of this invention are net-shapemolded. This means that the final shape of the article is determined bythe shape of the molding sections. No additional processing or toolingis required to produce the ultimate shape of the article.

[0035] Referring to FIGS. 1 and 2, the thermally-conductive andelectrically-insulating polymer composition of this invention can beover-molded an electronic device 12 to produce an integrated cover andelectronic device packaging assembly 10. (The electronic device 12 isshown as a resistor for illustration purposes only.) The polymercomposition of this invention is molded completely around electronicdevice 12 to substantially embrace it and seal it on all sides. Thepolymer composition is molded around and about electronic device 12 sothat it does not interfere with the interconnecting wire leads 14emanating therefrom. The polymer composition effectively seals theelectronic device 12 from exposure to dust and moisture.

[0036] Referring to FIG. 3, the moldable polymer composition 20 isover-molded the electronic device 12, emanation point 16, and upperportion 18 of the wire leads 14 to produce the package assembly 10. Byover-molding the polymer composition 20 directly onto the electronicdevice 12, emanation point 16, and upper portion 18 of the wire leads14, the composition 20 comes into and remains in direct contact withthese components. The critical wire leads 14 are allowed to protrudethrough the molded cover formed by the polymer composition 20. Thisover-molding process produces an effective hermetic seal around theelectronic device 12. The seal formed by polymer composition 20environmentally protects and electronically isolates the electronicdevice 12. The seal has high dielectric and mechanical strength.Further, the seal provides an effective means for dissipating heat fromthe electronic device 12, since the polymer composition 20 isthermally-conductive.

[0037] The over-molding process can be performed using techniques knownin the art. For example, the electrical device 12 can be placed into acavity of an injection-molding die (not shown) so that the wire leads 14are allowed to protrude therefrom. Once the electrical device 12 isinserted into the mold cavity, the cavity is flooded with the moldablepolymer composition of this invention. The integrated package assembly10 is then removed from the mold. The package assembly 10 is net-shapemolded meaning that the final shape of the assembly 10 is determined bythe shape of the mold. No further machine tooling or processing isrequired to produce the final shape of the molded package assembly 10.The package assembly 10 is ready “as is” for assembly into a finishedproduct (not shown).

[0038] Turning to FIG. 4, an alternative embodiment of the cover andelectronic device packaging assembly 100 is shown. Additional integratedheat dissipating members 102 are provided to further enhance the thermalconductivity of the package assembly 100. The heat dissipating members102 are shown in the form of fins in FIG. 4 for illustration purposesonly. The heat dissipating members 102 can have other structures. Forexample, the heat dissipating members 102 can be in the form of pins orother structures depending upon the intended application of the packageassembly 100. It should also be noted that heat dissipating members 102extend so as to surround an electronic device (not shown) embedded inthe package assembly 100. The direction of the heat dissipating members102 can be varied depending upon the intended application of theassembly 100.

[0039] The package assembly of the present invention has a wide range ofapplications. For example, the assembly can be used on any circuit boardor similar substrate where electrical device packages are needed. Theassembly can be used where the circuit board containing theheat-generating device is completely encased in a housing such as aPentium II chip configuration. In this arrangement (not shown), a heatsink assembly may be molded directly over the housing of theheat-generating device, and the step of providing a plastic casing overthe device can be eliminated.

[0040] The present invention is further illustrated by the followingexamples and test methods, but these examples and test methods shouldnot be construed as limiting the scope of the invention.

EXAMPLES

[0041] In the following Examples, a thermally-conductive compositioncomprising about 60 weight % boron nitride particles, about 30 weight %polyphenylene sulfide (PPS), and about 10 weight % of chopped glassbased on the weight of the composition was prepared, and variouselectrical properties of the composition were measured. The measurementswere taken on three (3) to five (5) samples of the polymer composition.The test methods used to measure the electrical properties and resultsare reported below.

[0042] Volume Resistivity and Surface Resistivity

[0043] The Volume Resistivity (ohms-cm) and Surface Resistivity (ohms)was measured using ASTM-D-257-99. The method involved placing eachspecimen individually in a Resistivity Cell connected to a HighResistance Meter. Five Hundred VDC were applied to the specimen for 60seconds. The resistance measurements were then taken. The resistivitywas calculated using the following formulas:

[0044] Volume Resistivity: $V = {\frac{19.6}{T} \times R}$

[0045] Where,

[0046] V=Volume Resistivity (ohms-cm);

[0047] R=measured volume resistance (ohms);

[0048] T=thickness (cm); and

[0049] 19.6=effective area of the guarded cell (cm²).

[0050] Surface Resistivity: S=18.8×R

[0051] Where,

[0052] S=Surface Resistivity (ohms);

[0053] R=Measured Surface Resistance (ohms); and

[0054] 18.8=effective area of the guarded cell. TABLE I VolumeResistivity Surface Resistivity Sample (ohms-cm) (ohms) 1 1.7 × 10¹⁶ 1.4× 10¹⁶ 2 1.8 × 10¹⁶ 7.5 × 10¹⁴ 3 2.1 × 10¹⁶ 1.2 × 10¹⁶

[0055] Dielectric Constant and Dissipation Factor

[0056] The Dielectric Constant and Dissipation Factor were measuredusing ASTM-D-150-98. The thickness of each specimen was measured andrecorded. Using an RF Impedance/Materials Analyzer, each specimen wasplaced in the testing fixture and the thickness measurement entered intothe analyzer. Each specimen was allowed to stabilize and the DielectricConstant and Dissipation Factor measurements were then taken at 1 MHz.Dimensions were recorded for each specimen for 100 Hz measurements. Thefrequency of the signal generator was varied around the calculatedresonant frequency of the empty cavity until the output power indicateda maximum value. An attenuation was introduced at a power level 3 dBdown from the resonant power level. Measurements of the resonantfrequency and “Q” Quality factor were taken on the empty cavity with andwithout the test specimen. Test specimens were then mounted into thetest cavity. The electric field inside the cavity was parallel to thelength of the test TABLE II Sample Dielectric Constant DissipationFactor @ 100 Hz 1 4.81 0.0104 2 4.72 0.0328 3 4.86 0.0216 @ 1 MHz 1 3.660.0017 2 3.70 0.0021 3 3.67 0.0031

[0057] Dielectric Strength

[0058] The Dielectric Strength was measured using ASTM-D-149-97a.Electrode size (2.0″): Each specimen was immersed in Dow Coming 704Silicone Oil. The cylindrical probes were placed in contact with thespecimen. The voltage was then increased at a rate of 500 volts/seconduntil breakdown or arc over occurred. TABLE III Breakdown ThicknessSample Voltage (inches) Volts/mil 1 44,500 0.0504 883 2 45,200 0.0503899 3 44,500 0.0498 894

[0059] Comparative Tracking Index

[0060] The Comparative Tracking Index was measured using ASTM-D-3638-98.The test area was cleaned to remove any dust, dirt, fingerprints,grease, oil, etc. Two opposing platinum electrodes were placed 4 mmapart on a flat horizontal surface of the specimen. The electrodes weresupplied with a sinusoidal voltage, at a frequency of 60 Hz. A variableresistor was connected to the system in order to adjust the currentbetween any short circuit in the electrodes. The surface of the specimenbetween the electrodes was wetted with drops of an AmmoniumChloride/Distilled Water solution. The drops fell centrally between theelectrodes from a height of 40 mm. The drop size was regulated inaccordance with the specification. The test was started by dripping thesolution onto the surface of the test sample. Failure occurred when acurrent of 0.5 A or more flowed for at least 2 seconds in a conductionpath between the electrodes, or if the specimen burned without releasingthe over-current relay. TABLE IV Sample Comparative Tracking Index(Volts) 1 600 2 525 3 600 4 600 5 575

[0061] Arc Resistance

[0062] The Arc Resistance was measured using ASTM-D-495-99. Eachspecimen was inserted into the tester with the electrode spacing set at0.25″. The arc tester was set in the automatic mode with 105 to 115V.The timer was set to 0 seconds. The tester was then started using thefollowing sequence: Step Current, mA Time Cycle Total Time, (sec) ⅛ 1010 0.25 sec/1.75 sec  60 ¼ 10 10 0.25 sec/0.75 sec 120 ½ 10 10 0.25sec/0.25 sec 180 10 10 continuous 240 20 20 continuous 300 30 30continuous 360 40 40 continuous 420

[0063] When the arc disappeared and tracking occurred, the timer isstopped and the time was recorded. The electrodes were then cleaned forthe next specimen. TABLE V (Results) Sample Arc Resistance (Seconds) 1303.9 2 302.1 3 302.9

[0064] Hot Wire Ignition

[0065] The Hot Wire Ignition was measured using ASTM-D-3874-97. Thecenter portion of the specimens were wrapped with an annealed test wire,using a winding fixture five complete turns were spaced ¼ inch apart.The free ends of the wire were connected to the test circuit, makingsure the test specimen's length and width are horizontal. The circuitwas then energized and the timer was stated. The test specimen continuedto heat, until ignition occurred. The power was then shut off and theelapsed time recorded. The test is discontinued if the specimen fails toignite within 120 seconds. TABLE VI Sample Time to Ignition (seconds)1 >120 2 >120 3 >120 4 >120 5 >120

[0066] High Voltage Arc Tracking Rate

[0067] The High Voltage Arc Tracking Rate was measured using U1746A.Each test specimen was clamped in position under the electrodes. Theelectrodes were placed on the surface of the test specimen and spaced4.0 mm from tip to tip. The circuit was then energized. As soon as thearc tracking appeared on the surface of the test specimen, the movableelectrode was drawn away as quickly as possible while still maintainingthe arc tracking. If the arc extinguishes, the spacing between theelectrodes was shortened as quickly as possible until the arc wasreestablished. Immediately following the reestablishment of the arc, theelectrodes were then again withdrawn as quickly as possible. Thisprocess was repeated for 2 minutes of accumulated arcing time. Thelength of the conductive path or track was measured and the trackingrate was determined by dividing the length of the path in millimeters bythe 2 minute arcing time. Any ignition of the test specimen, or a holeburned through the sample, was not recorded. High-voltagearc-tracking-rate performance level categories (PLC) Range − trackingrate (mm/min) Assigned PLC 0 < TR ≦ 10 0 10 < TR ≦ 25.4 1 25.4 < TR ≦ 802 80 < TR ≧ 150 3 150 < TR 4

[0068] TABLE VII (Results) Tracking Rate = 60L/t Sample (mm/min) 1 0 2 03 0

[0069] High Voltage Arc Resistance To Ignition

[0070] Each test specimen was clamped in position under the electrodes.The electrodes were placed on the surface of the test specimen andspaced 4.0±0.1 mm from tip to tip. The circuit was then energized. Thetest was continued for 5 minutes, or until ignition, or a hole throughthe specimen occurs. High voltage arc resistance to ignition performancelevel categories (PLC) HVAR Range − Assigned Mean Time to Ignition (sec)PLC 300 ≦ TI 0 120 ≦ TI < 300 1 30 ≦ TI < 120 2 0 ≦ TI < 30 3

[0071] TABLE VIII (Results) Sample Time to Ignite (sec) 1 >300 2 >300 3>300

[0072] It is appreciated by those skilled in the art that variouschanges and modifications can be made to the illustrated embodimentswithout departing from the spirit of the invention. All suchmodifications and changes are intended to be covered by the appendedclaims.

What is claimed is:
 1. A thermally-conductive, electrically-insulatingpolymer composition, comprising: a) 20% to 80% by weight of a polymermatrix, and b) 20% to 80% by weight of a thermally-conductive,electrically-insulating ceramic material.
 2. The composition of claim 1,wherein the polymer matrix is a thermoplastic polymer.
 3. Thecomposition of claim 2, wherein the polymer matrix is polyphenylenesulfide.
 4. The composition of claim 1, wherein thethermally-conductive, electrically-insulating ceramic material isselected from the group consisting of alumina, calcium oxide, titaniumoxide, silicon oxide, zinc oxide, silicon nitride, aluminum nitride,boron nitride, and mixtures thereof.
 5. The composition of claim 1,further comprising a reinforcing material.
 6. The composition of claim5, wherein the reinforcing material is glass.
 7. An electronic devicepackage assembly, comprising: an electronic device having a front side,rear side, left side, right side, bottom side, and top side; a moldedcover disposed about said electronic device and in thermal communicationwith at least said front side, rear side, left side, right side, and topside of said electronic device, and at least two wire leads, said wireleads emanating from said electronic device and protruding through saidmolded cover, said molded cover comprising a thermally-conductive,electrically-insulating polymer composition comprising: a) 20% to 80% byweight of a polymer matrix, and b) 20% to 80% by weight of athermally-conductive, electrically-insulating material.
 8. The packageassembly of claim 7, wherein the polymer matrix is a thermoplasticpolymer.
 9. The package assembly of claim 8, wherein the polymer matrixis polyphenylene sulfide.
 10. The package assembly of claim 7, whereinthe thermally-conductive, electrically-insulating ceramic material isselected from the group consisting of alumina, calcium oxide, titaniumoxide, silicon oxide, zinc oxide, silicon nitride, aluminum nitride,boron nitride, and mixtures thereof.
 11. The package assembly of claim7, further comprising a reinforcing material.
 12. The package assemblyof claim 11, wherein the reinforcing material is glass.
 13. A method ofmanufacturing an electronic device package assembly, comprising thesteps of: a) providing an electronic device having a front side, rearside, left side, right side, bottom side and top side and at least twowire leads, said wire leads emanating from said electronic device; andb) molding a thermally-conductive, electrically-insulating polymercomposition over the electronic device so that the composition is incontact with at least the front side, rear side, left side, right side,and top side of the electronic device, and the wire leads protrudethrough the composition, said polymer composition comprising: a) 20% to80% by weight of a polymer matrix, b) 20% to 80% by weight of athermally-conductive, electrically-insulating material.
 14. The methodof claim 13, wherein the polymer matrix is a thermoplastic polymer. 15.The method of claim 14, wherein the polymer matrix is polyphenylenesulfide.
 16. The method of claim 13, wherein the thermally-conductive,electrically-insulating ceramic material is selected from the groupconsisting of alumina, calcium oxide, titanium oxide, silicon oxide,zinc oxide, silicon nitride, aluminum nitride, boron nitride, andmixtures thereof.